Chloroplatinic acid

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Dihydrogen hexachloroplatinate (IV) hexahydrate
Dihydrogen hexachloroplatinate (IV) hexahydrate
IUPAC name Dihydrogen hexachloroplatinate (IV)
hexahydrate
Other names Chloroplatinic Acid
Identifiers
CAS number [16941-12-1]
RTECS number TP1510000
Properties
Molecular formula H2PtCl6·(H2O)6
Molar mass 517.891 g/mol
Appearance Reddish brown solid
Density 2.431 g/cm³, solid
Melting point

60 °C (333 K)
Boiling point

decomp
Solubility in water highly sol
Structure
Crystal structure Anti-fluorite.
Coordination
geometry		 octahedral
Dipole moment 0 D
Hazards
MSDS External MSDS
NFPA 704
0
3
0
 
R-phrases R34, R42, R43
S-phrases S22, S26, S36, S37, S39, S45
Related compounds
Other anions H2PdCl6 (unstable) Hexachloropalladic acid
Other cations K2PtCl6 Potassium hexachloroplatinate
K2PtCl4 Potassium tetrachloroplatinate
(NH4)2PtCl6 Ammonium hexachloroplatinate,
Rb2PtCl6 Rubidium hexachloroplatinate,

Cs2PtCl6 Caesium hexachloroplatinate
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Dihydrogen hexachloroplatinate(IV) hexahydrate is the chemical compound with the formula H2PtCl6·(H2O)6. Also known as hexachloroplatinic acid or chloroplatinic acid, it is one of the most readily available soluble compounds of platinum. Unusually, it is rarely obtained in the pure state. The commercial product is the oxonium salt of the hexachloroplatinate(IV) anion. Therefore, the correct formula is [H3O]2[PtCl6]·4H2O.(5,6) The related palladium compound,[H3O]2[PdCl6] is extremely unstable and has not been isolated in pure form.[1]

Contents

[edit] Production

Chloroplatinic acid is produced by dissolving platinum metal sponge in aqua regia. This reaction is rumored to produce nitrogen-containing platinum compounds, but the product is H2PtCl6. Chloroplatinic acid is brownish-red, and can be isolated by evaporating this solution to a syrup.[2]

Pt + 4 HNO3 + 6 HCl → H2PtCl6 + 4 NO2 + 4 H2O

Alternative methods have been heavily investigated, but the older literature can be unreliable.[3]

[edit] Applications

[edit] Potassium determination

Chloroplatinic acid was popularized for the determination of potassium. The potassium is selectively precipitated as potassium chloroplatinate. Determinations were done in 85% (v/v) alcohol solutions with excess platinate ions, and the precipitated product was weighed. Potassium could be detected for solutions as dilute as 0.02 to 0.2% (m/v).[4]

This method for determination of potassium was advantageous vs. the cobaltinitrite method used previously, since it required a single precipitation reaction.[citation needed] Today, the concentration of potassium is determined with an ion-selective electrode. These modern methods remain subject to interference.

[edit] Catalysis

Like many platinum compounds, chloroplatinic acid is used in catalysis. This compound was first reported by John Speier and colleagues from Dow Corning Corporation to catalyze the reaction of silyl hydrides with olefins, hydrosilylation.(3) Typical of his reactions, Speier used isopropanol solutions containing trichlorosilane (SiHCl3), and methyldichlorosilane (CH3HSiCl2), with pentenes. Prior work on the addition of silanes to alkenes required radical reactions that were inefficient.[5][6] It is generally agreed that chloroplatinic acid is a catalyst precursor, and more recent discussions have considered a possible role for colloidal platinum or zero-valent complexes.[7]

[edit] Related compounds

Chloroplatinic acid prepared from aqua regia is occasionally contaminated with (NO)2PtCl6. This species is obtained by the reaction of nitrosyl chloride and Pt metal.[8]

[edit] References

  1. ^ Greenwood, N.N.; Earnshaw, A. (1997). Chemistry of the Elements, Second Edition, New York: Elsevier Butterworth-Heinemann. ISBN 978-0750633659. 
  2. ^ George B. Kauffman (1967). "Ammonium Hexachloroplatinate(IV)". Inorganic Syntheses 9: 182–185. doi:10.1002/9780470132401.ch51. 
  3. ^ Paul Rudnick and R. D. Cooke (1917). "The Preparation of Hydrochloroplatinic Acid by means of Hydrogen Peroxide". J. Am. Chem. Soc. 39 (4): 633–635. doi:10.1021/ja02249a011. 
  4. ^ G. F. Smith, J. L. Gring (1933). "The Separation and Determination of the Alkali Metals Using Perchloric Acid. V. Perchloric Acid and Chloroplatinic Acid in the Determination of Small Amounts of Potassium in the Presence of Large Amounts of Sodium". J. Am. Chem. Soc. 55 (10): 3957–3961. doi:10.1021/ja01337a007. 
  5. ^ J. L. Speier, J. A. Webster, G. H. Barnes (1957). "The Addition of Silicon Hydrides to Olefinic Double Bonds. Part II. The Use of Group VIII Metal Catalysts". J. Am. Chem. Soc. 79 (4): 974–979. doi:10.1021/ja01561a054. 
  6. ^ John C. Saam, John L. Speier (1958). "The Addition of Silicon Hydrides to Olefinic Double Bonds. Part III. The Addition to Non-terminal Olefins in the Presence of Chloroplatinic Acid". J. Am. Chem. Soc. 80 (15): 4104. doi:10.1021/ja01548a073. 
  7. ^ L. N. Lewis, K. G. Sy, G. L. Bryant and P. E. Donahue (1991). "Platinum-catalyzed hydrosilylation of alkynes". Organometallics 10 (10): 3750–3759. doi:10.1021/om00056a055. 
  8. ^ R. T. Moravek, G. B. Kauffman and T. Mahmood (1967). "Nitrosyl Hexachloroplatinate(IV)". Inorganic Syntheses 9: 217–220. doi:10.1002/9780470132555.ch63. 

[edit] Further reading

  • A. E. Schweizer, G. T. Kerr (1978). "Thermal Decomposition of Hexachloroplatinic Acid". Inorg. Chem. 17 (8): 2326–2327. doi:10.1021/ic50186a067. 
  • Holleman, Wiberg (2001). Inorganic Chemistry, First Edition, New York: Academic Press.